Camshaft adjusters of this type are used to change the timing of gas exchange valves of an internal combustion engine during engine operation for the purpose of improving the consumption values and the operating behavior of the internal combustion engine.
One specific embodiment, which has been proven and tested in practice, is a camshaft adjuster designed as a vane adjuster, including a stator and a rotor which delimit an annular space, which is divided into two working chambers by vanes. A hydraulic medium may be optionally applied to the working chambers, which is supplied to the working chambers on one side of the vanes of the rotor from a pressure medium reservoir in a pressure medium circuit via a pressure medium pump, and which is fed back into the pressure medium reservoir from the working chambers on the particular other side of the vanes. The working chambers whose volume is increased have an operating direction which is opposite the operating direction of associated opposite working chambers. Due to the operating direction, a rotation of the rotor relative to the stator may be triggered in the clockwise or counterclockwise direction. The control of the pressure medium flow, and thus the adjusting movement of the camshaft adjuster, includes a hydraulic multi-way switching valve, with the aid of which flow-through openings may be blocked or unblocked as a function of a position of a valve body.
One problem with these camshaft adjusters is that they are not yet fully filled with pressure medium in a start phase or have not yet been emptied. When the engine starts, if the oil pressure within the internal combustion engine has not yet been built up, the alternating torques applied by the camshaft may trigger uncontrolled movements of the rotor with respect to the stator, which may result in increased wear and an undesirable noise development. To avoid this problem, it is known to provide a locking device between the rotor and the stator, which locks the rotor when the internal combustion engine is turned off in a rotation angle position with respect to the stator which is favorable for startup.
Locking devices of this type preferably include spring-loaded locking pins, which successively lock into locking gates provided on the sealing cover or the stator when the rotor rotates. Before a central locking position is reached, a rotation of the rotor in the direction of the central locking device is possible, but a rotation of the rotor in the opposite direction is blocked. After the internal combustion engine has warmed up and/or the camshaft adjuster has been completely filled with pressure medium, the locking pins are forced out of the locking gates, actuated by the pressure medium, so that the rotor is subsequently able to properly rotate with respect to the stator to adjust the rotation angle position of the camshaft.
A control device assigned to the vanes is also known, whose control pins are positioned in the vane separating the working chambers. A fluidic connection of two oppositely acting working chambers may be established with the aid of this control device. The control pins are moved against a spring force by the application of pressure medium. The control pins may be arranged in such a way that a fluidic connection between the working chambers is interrupted upon an application of pressure medium. When the internal combustion engine is turned off, both the spring-loaded locking pins of the locking devices and the control pins of the control device are placed from an unlocking position into an unpressurized locking position by the spring force.
A hydraulic camshaft adjuster designed as a vane adjuster is known from the publication U.S. Pat. No. 6,684,835 B2, whose central locking action takes place when the engine is turned off. An electronic control unit detects a signal which is generated when the engine is turned off as well as signals that represent the status of the stator relative to the rotor. An electrical control valve includes five ports, of which one port accommodates the oil inflow from the lubricating oil circuit of the engine or the pressure medium pump, one port connects the solenoid valve to all locking pistons or locking pins, and two ports connect the solenoid valve to working chambers A and B of the camshaft adjuster and one tank port is provided for the oil outflow from the solenoid valve.